Diseases of the central nervous system such as epilepsy, Parkinson's disease or obsessive compulsive diseases are inter alia treated by means of direct electrical stimulation of the brain. For this purpose, electrodes are implanted into the target areas and are electrically connected to corresponding implant systems under the skin. Electrical stimuli are transmitted to the target area via the implant system. In electrical stimulation, in particular the observation of the charge density and thus of the charge amount per pulse is an important criterion to avoid long-term damage to the tissue in the course of the therapeutic stimulation. The transmission of the charge amount is typically limited by a coupling capacitor. One such coupling capacitor, e.g. having a capacitance of 100 nF and a charge transmission of a maximum of 1 μC is required per stimulation contact.
Single capacitors or an array of capacitors have previously typically been used for the implementation of the coupling capacitors. The capacitors are usually ceramic-based capacitors having a capacitance of 100 nF or more, for example. The value of the capacitance is substantially determined by the supply voltage of the implant and by the surface of the stimulation contacts. If a higher supply voltage or a smaller contact surface is selected, the capacitance can be selected as lower.
More recent electrode designs provide a larger number of electrode contacts, for example 8, 16 or 40 contacts. An implant to which such an electrode is connected accordingly has to have a large number of coupling capacitors. The coupling capacitors take up a large space within the implant due to their large number and therefore limit the miniaturization of the implant in order, for example, to select a favorable implantation site in the region of the cranium or to design the implant such that it is not visible from the outside. In addition, the risk of an inflammation reaction or of a rejection of the implant in the patient is the greater, the larger the implant is.
The large number of electrical contacts furthermore has to be led out of the interior of the hermetically closed implant housing. Such cable passages are frequently called “feedthroughs” in the technical literature. Conventional feedthroughs from the interior of the implant to the terminals of the electrode are typically realized by the integration of one or more ceramic components in openings of the housing that typically comprises titanium. The size and construction shape of the implant are hugely restricted by such feedthroughs. Furthermore, the location of the feedthrough represents a critical region that can be the site of a leak at which complications or even injury to the patient can occur due to the penetration of bodily fluids.